Compressors and systems incorporating compressors have been developed and are often utilized in a myriad of industrial processes (e.g., petroleum refineries, offshore oil production platforms, and subsea process control systems). Conventional compressors may be configured to compress a process fluid by applying kinetic energy to the process fluid to transport the process fluid from a low pressure environment to a high pressure environment. The compressed process fluid discharged from the compressors may be utilized to efficiently perform work or operate one or more downstream processes. Improvements in the efficiency of conventional compressors has increased the application of the compressors at various oil production sites. Many of the oil production sites (e.g., offshore), however, may be constrained or limited in space. Accordingly, there is an increased interest and demand for smaller and lighter compressors, or compact compressors. In addition to the foregoing, it is often desirable that the compact compressors be capable of achieving higher compression ratios (e.g., 10:1 or greater) for increased production while maintaining a compact footprint.
To achieve the higher compression ratios, conventional compact compressors may often utilize an impeller and a balance piston integrally formed with the impeller. The impeller may be coupled with a rotary shaft configured to rotate within the compact compressors to accelerate the process fluid, and the integral balance piston may be configured to balance axial thrusts generated by the rotation of the impeller. However, as the impeller rotates to accelerate the process fluid at least a portion of the compressed process fluid may leak or flow pass the impeller and the balance piston via radial clearances, thereby reducing the efficiency of the compact compressors.
In view of the foregoing, conventional compact compressors may often utilize balance piston seals (e.g., hole pattern seals) disposed about the balance piston to manage the leakage flow of the process fluid through the radial clearances. However, as the impeller accelerates to the rotational speeds necessary to achieve the higher compression ratios (e.g., 10:1 or greater), thermal energy (e.g., heat of compression) and/or centrifugal forces may cause the impeller and the balance piston to expand or grow radially outward. Additionally, the thermal energy generated from the compression of the process fluid may also cause the thermal expansion of the balance piston seal. While the rotary shaft may at least partially maintain the alignment of the impeller and the balance piston, the thermal expansion of the balance piston seal may cause misalignment of the balance piston seal relative to the balance piston. For example, the thermal expansion of the balance piston seal may cause the balance piston seal to become radially offset from the balance piston, thereby resulting in the eccentric rotation of the balance piston relative to or within the balance piston seal. The eccentric rotation of the balance piston within the balance piston seal may decrease operational efficiencies, and may ultimately result in damage to the compact compressors and/or components thereof. For example the eccentric rotation may cause incidental contact between the rotating balance piston and the balance piston seal, which may result in damage to the balance piston and/or the balance piston seal.
What is needed, then, is an improved balance piston seal assembly and method for controlling a radial clearance between a balance piston and a balance piston seal.